The present invention relates generally to an imaging process. More specifically, the invention relates to an application system for applying a two-step transfix process whereby a hot melt ink is applied onto an elastomer transfer surface and then transferred to a receiving substrate, followed by re-transfixing the hot melt ink by pulling the receiving substrate through a duplex path.
For printing in a solid-ink printer, a common method of applying droplets of ink onto a piece of paper is to directly print the image onto the paper, i.e., a process known as direct printing. However, direct printing has many disadvantages. First, the head to paper gap must be adjusted for different media in order to control drop position. Second, there is the well-known paper hand-off problem between the rollers that guide the paper, because of the large size of the head. Third, there is a concern that head reliability will decrease because the paper is near the head. Also, to maximize print speed, many direct print architectures deposit the image bi-directional, which introduces image artifacts and color shifts. These problems are addressed with an offset process. In this process, the ink is first applied to a rotating drum and is then transferred off the drum and fixed into the paper in a single pass. This process is known as a transfix process or a transfuse process. Therefore, a single drum surface transfers the image, spreads the pixels, penetrates the pixels into the media, and controls the topography of the ink to increase paper gloss and transparency haze. The process requires a delicate balance of drum temperature, paper temperature, transfix load, and drum and transfix roller materials and properties in order to achieve image quality. These combined requirements reduce the drum material possibilities mainly due to wear of weaker materials, which result in gloss and haze degradation. There are also undesired print and image quality trade-offs, which must be made when optimizing a printer for customer usage. For instance, between good gloss versus good image transfer.
Ink jet printing systems utilizing intermediate transfer ink jet recording methods, such as that disclosed in U.S. Pat. No. 5,389,958 entitled IMAGING PROCESS and assigned to the assignee of the present application (the ""958 patent) is an example of an indirect or offset printing architecture that utilizes phase change ink. A release agent application defining an intermediate transfer surface is applied by a wicking pad that is housed within an applicator apparatus. Prior to imaging, the applicator is raised into contact with the rotating drum to apply or replenish the liquid intermediate transfer surface.
Once the liquid intermediate transfer surface has been applied, the applicator is retracted and the print head ejects drops of ink to form the ink image on the liquid intermediate transfer surface. The ink is applied in molten form, having been melted from its solid state form. The ink image solidifies on the liquid intermediate transfer surface by cooling to a malleable solid intermediate state as the drum continues to rotate. When the imaging has been completed, a transfer roller is moved into contact with the drum to form a pressurized transfer nip between the roller and the curved surface of the intermediate transfer surface/drum. A final receiving substrate, such as a sheet of media, is then fed into the transfer nip and the ink image is transferred to the final receiving substrate.
To provide acceptable image transfer and final image quality, an appropriate combination of pressure and temperature must be applied to the ink image on the final receiving substrate. U.S. Pat. No. 6,196,675 entitled APPARATUS AND METHOD FOR IMAGE FUSING and assigned to the assignee of the present application (the ""675 patent) discloses a roller for fixing an ink image on a final receiving substrate. The preferred embodiment of the roller is described in the context of an offset ink jet printing apparatus similar to the one described in the ""958 patent. In this embodiment, an apparatus and related method for improved image fusing in an ink jet printing system are provided. An ink image is transferred to a final receiving substrate by passing the substrate through a transfer nip. The substrate and ink image are then passed through a fusing nip that fuses the ink image into the final receiving substrate. Utilizing separate image transfer and image fusing operations allows improved image fusing and faster print speeds. The secondary fusing operation enables the image transfer process to use reduced pressures, whereby the load on the drum and transfer roller is reduced. However, while the simultaneous transfer and fusing outlined in this architecture has many advantages, the separate fuser does necessitate the requirement for additional components, i.e., the fuser system. Additional components offer greater flexibility in print and image quality and print speed; however, it also leads to higher cost, complexity and weight. For some markets, such as the consumer market, the design is driven more by cost than print speed and so the addition of a separate fuser is cost prohibitive. Therefore what is needed is a transfer surface application system that achieves the benefits of the separate transfer and fuse architecture without the drawbacks of previous application systems using a separate fusing mechanism.
It is an object of the present invention to provide an improved imaging method and apparatus which allows high quality imaging on a variety of transparency media wherein lensing of an image is greatly reduced, which reduces haze in transparencies.
It is an object of the present invention to provide an improved imaging method and apparatus which allows high quality imaging on a variety of paper wherein the gloss of the media is greatly increased.
It is another object of the present invention to provide an improved imaging apparatus and method for a combination soft drum and hard roller for near perfect image transfer.
Accordingly, the present invention is an application system for applying a two-step transfix process whereby an ink image is applied onto an intermediate transfer surface and then transferred to a receiving substrate, followed re-transfixing the ink image by pulling the receiving medium back through a duplex path. The system includes an applicator assembly for uniformly distributing a liquid layer onto a support surface defining an elastomer release surface to produce the intermediate transfer surface. The system uses the elastomer transfer surface in combination with a hard transfix roller and an integrated duplex path for near perfect image transfer of the ink image onto the receiving substrate and post fusing of the media without the need for a separate fusing mechanism. Lensing of the ink image is greatly reduced on transparencies and/or gloss of the ink surface is greatly increased on paper.
Still other aspects of the present invention will become apparent to those skilled in this art from the following description, wherein there is shown and described a preferred embodiment of this invention by way of illustration of one of the modes best suited to carry out the invention. The invention is capable of other different embodiments and its details are capable of modifications in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive.